Microfluidic Device for Monitoring Catalytic Events on Armored Bubbles

Low cost fabrication of microfluidic paper-based analytical devices with water-based polyurethane acrylate and their application for bacterial detection

This study presents a method for the fabrication of solvent‐resistant poly(dimethylsiloxane) (PDMS) microfluidic devices by coating the microfluidic channel with a hybrid inorganic/organic polymer (HR4). This modification dramatically increases the resistance of PDMS microfluidic channels to various solvents, because it leads to a significant reduction in the rate of solvent absorption and consequent swelling. The compatibility of modified PDMS with a wide range of solvents is investigated by evaluating the swelling ratio measured through weight changes in a standard block. The HR4‐modified PDMS microfluidic device can be applied to the formation of water‐in‐oil (W/O) and oil‐in‐water (O/W) emulsions. The generation of organic solvent droplets with high monodispersity in the microfluidic device without swelling problems is demonstrated. The advantage of this proposed method is that it can be used to rapidly fabricate microfluidic devices using the bulk properties of PDMS, while also increasing their resistance to various organic solvents. This high compatibility with a variety of solvents of HR4‐modified PDMS can expand the application of microfluidic systems to many research fields.

In this study, we developed microfluidic paper-based analytical devices (μPADs) for the determination of antioxidant vitamins. The proposed μPADs utilize the reduction of metal ions by hydrophilic and hydrophobic antioxidant vitamins, which is followed by colorimetric reactions with chelating reagents. Hydrophilic vitamin C reduces Fe(III) to Fe(II) and forms a stable Fe(II)-bathophenanthroline complex in an aqueous solution. By contrast, this complex is unstable in organic solvents, and hydrophobic vitamin E requires Fe(III) and bathophenanthroline to be replaced with Cu(II) and bathocuproine. In these results, the relationship between the logarithm of a vitamin's concentration and its color intensity was linear and ranged from 4.4 to 35mgL-1 for ascorbic acid and 50-200mgL-1 for α-tocopherol. The limits of detection, estimated from the standard deviation of blank samples, were 3.1mgL-1 for ascorbic acid and either 27mgL-1 (in hexane) or 48mgL-1 (in ethanol) for α-tocopherol. The proposed method was used to quantify vitamin C in bell peppers, mandarin oranges, kiwifruit, and lemons, as well as vitamin E in almonds, almond milk, and dietary supplements. The results demonstrate the effectiveness of these μPADs for the practical analysis of antioxidant vitamins in food samples.

A central challenge in the development of drug-encapsulated polymeric nanoparticles is the inability to control the nanoparticle physicochemical properties that affect their biodistribution, drug release, and efficacy. Nanoparticles may be developed by mixing and nanoprecipitation of polymers and drugs dissolved in organic solvents with non-solvents. Inadequate control over this mixing process is a source of variability in the synthesis of these nanoparticles by nanoprecipitation. We demonstrate that rapid and tunable mixing through hydrodynamic flow focusing in a microfluidic device can be used to control nanoprecipitation of poly(lactic-co-glycolic acid)-bpoly(ethylene glycol) (PLGA-PEG) diblock copolymers as a model polymeric biomaterial for drug delivery.

Here we propose a simple but efficient method to produce collagen hydrogel microfibers using a microfluidic spinning system and a formation technique of collagen gels in a phosphate buffer. An aqueous solution of type I collagen was introduced into the microfluidic devices together with a phosphate buffer and distilled water. Parallel laminar flow was stably formed in the microchannel, and the collagen solution was transformed into microfibers with a uniform diameter. We examined factors affecting the fiber diameter and successfully obtained microfibers with a diameter from ~8 to ~30 μm. In addition, we confirmed that cells adhered on the surface of the microfibers and proliferated after culturing for several days. The presented method is advantageous because it enables the production of collagen microfibers under a wet condition without using complicated operations, organic solvents, or crosslinking reagents.

Magnetite decorated with gold nanoparticles (Fe3O4-AuNPs) is a ferrimagnetic material with unprecedented applications in immunosensors, as a contrast agent for imaging diagnosis, and for the photothermal ablation of tumor cells. Here, we show the preparation of controlled amounts of Fe3O4-AuNPs without organic solvents, surfactants, or heat treatment. For this, we have developed a customized natural-rubber-based microfluidic device (NRMD) as a flexible lab-on-a-chip for the decoration of Fe3O4 with AuNPs. With a novel NRMD configuration, monodisperse Fe3O4-NPs (ϕ = 10 nm) decorated with AuNPs (ϕ = 4 nm) were readily obtained. The AuNPs were homogenous in terms of their size and their distribution on the Fe3O4-NP surfaces. Furthermore, the lab-on-a-chip was projected with an internal system for magnetic separation, an innovation in terms of aqueous/carrier phase separation. Finally, the nanomaterials produced with this NRMD are free of organic solvents and surfactants, allowing them to be used directly for medical applications.

We report a centrifugal microfluidic device that automatically performs sample preparation under steady-state rotation for clinical applications using mass spectrometry. The autonomous microfluidic device was designed for the control of liquid operation on centrifugal hydrokinetics (CLOCK) paradigm. The reported device was highly stable, with less than 7% variation with respect to the time of each unit operation (sample extraction, mixing, and supernatant extraction) in the preparation process. An agitation mechanism with bubbling was used to mix the sample and organic solvent in this device. We confirmed that the device effectively removed the protein aggregates from the sample, and the performance was comparable to those of conventional manual sample preparation procedures that use high-speed centrifugation. In addition, probe electrospray ionization mass spectrometry (PESI-MS) was performed to compare the device-treated and manually treated samples. The obtained PESI-MS spectra were analyzed by partial least squares discriminant analysis, and the preparation capability of the device was found to be equivalent to that of the conventional method.

Hyper-cross-linked thin polydimethylsiloxane films

The development of miniaturized devices for studying zebrafish embryos has been limited due to complicated fabrication and operation processes. Here, we reported on a microfluidic device that enabled the capture and culture of zebrafish embryos and real-time monitoring of dynamic embryonic development. The device was simply fabricated by bonding two layers of polydimethylsiloxane (PDMS) structures replicated from three-dimensional (3D) printed reusable molds onto a flat glass substrate. Embryos were easily loaded into the device with a pipette, docked in traps by gravity, and then retained in traps with hydrodynamic forces for long-term culturing. A degassing chamber bonded on top was used to remove air bubbles from the embryo-culturing channel and traps so that any embryo movement caused by air bubbles was eliminated during live imaging. Computational fluid dynamics simulations suggested this embryo-trapping and -retention regime to exert low shear stress on the immobilized embryos. Monitoring of the zebrafish embryogenesis over 20 h during the early stages successfully verified the performance of the microfluidic device for culturing the immobilized zebrafish embryos. Therefore, this rapid-prototyping, low-cost and easy-to-operate microfluidic device offers a promising platform for the long-term culturing of immobilized zebrafish embryos under continuous medium perfusion and the high-quality screening of the developmental dynamics.

Introduction Despite certain advances in medicine cancer diseases are still an urging problem. There is a great need to develop new or improve already existing anticancer therapies. Due to its high surface area, abundance of oxygen groups and affinity towards cancer cells, graphene oxide (GO) has a great potential to found an application as a novel drug carrier in photodynamic therapy (PDT).In this study we examined the efficiency of photodynamic therapy using meso-tetraphenylporphirin (TPP) as a photosensitizer and modified graphene oxide as a drug carrier. Graphene oxide was functionalized with ethylenediamine via carbon – nitrogen bond (GO1) and with tetraethylenepentamine (GO2). The cytotoxicity tests and cellular uptake examination were conducted using coculture of normal (HMF) and cancer (MCF-7) breast cell lines. Cells were cultured in a microfluidic Lab-on-a-chip device as monolayer (2D) and spheroids (3D). The use of the microfluidic device provided conditions which better mimicked in vivo environment than standard macroscale cell cultures. The design of the microfluidic device A main microchannel allowed to introduce solutions and cell suspensions into microfluidic device. In order to avoid presence of air bubbles it was equipped with a venting system. The main microchannel split into two pairs of parallel microchannels with three microchambers in each channel. In six microchambers cells were cultured as spheroids and in the other six as monolayer. Microchambers for spheroid culture contained 19 microwells with semicircular bottom. In addition their surface was modified with poli(vinylalcohol) (PVA). Microchambers designed for monolayer culture had flat bottom and their surface was modified with fibronectin. The layout of microchambers corresponded to layout of wells in 384-well plate. Therefore, spectrofluorimetric measurements could be performed in standard multi-well plate reader using dedicated chip holder. The design of the microfluidic device is illustrated on the Figure 1. Method On the first day of the experiment the microfluidic device was fabricated and modified with PVA and fibronectin. Then, cell suspension was introduced into the microsystem and incubated for 24h. After that GO1-TPP or GO2-TPP and negative control solution were introduced into the. In order to evaluate efficiency of photodynamic therapy using GO1-TPP and GO2-TPP cell viability, cellular uptake and reactive oxygen species (ROS) generation were examined. Cell cultures were irradiated (640 nm, 40 mWcm-2, 10 min.). Then cell cultures were incubated for another 24h. After that photocytotoxicity was evaluated using AlamarBlue® test. TPP accumulation in cells were measured 24h after introduction of GO1-TPP or GO2-TPP solutions into microsystem. Cell culture medium was changed to fresh and fluorescence intensity of TPP was measured (EEX=514 nm, EEM=650 nm). In addition, intracellular localization and uptake ware examined using confocal microscopy. Reactive oxygen species generation was measured 24h after introducing examined compounds into the microsystem. Dichloro-dihydro-fluorescein diacetate (DCFH-DA) assay was used to examine ROS generation before and after cell irradiation (640 nm, 40 mWcm-2, 10 min.). All results were presented as a percentage of negative control. Results and Conclusions Non-irradiated cells incubated with GO1-TPP and GO2-TPP solutions did not exhibit significant decrease in cell viability. However, examined compounds in the same samples after irradiation showed enhanced cytotoxicity towards cell cultures. In addition, efficiency of photodynamic using GO1-TPP and GO2-TPP was greater comparing to free PTT. Cellular uptake studies are consistent with these results. Only TPP bound to the drug carrier was able to penetrate cell membrane. What is more, ROS generation was also greater in case of GO1-TPP and GO2-TPP comparing to free TPP. What is interesting 2D cell culture (monolayer) was more resistant to examined compounds than 3D cell culture (spheroids). This shows the importance of applying various cellular models in preclinical studies. The results of our experiment shows that examined graphene oxide derivatives can be efficient drug carriers in PDT. This work was financially supported within a frame of OPUS 11 program No. UMO-2016/21/B/ST5/01774. Figure 1

Development of pH sensitive biocompatible block copolymer polymersomes, which are stable in physiological conditions, is enabling the intracellular delivery of water soluble drugs and proteins. As a result, it is becoming increasingly important to develop robust production methods to enhance the polymersome encapsulation efficiency. One way that this could be achieved is through production in microfluidic devices that potentially offer more favourable conditions for encapsulation. Here a flow focussing microfluidic device is used to induce self-assembly of poly(2-(methacryloyloxy)ethyl phosphorylcholine)-poly(2-(diisopropylamino)ethyl methacrylate) (PMPC-b-PDPA) block copolymer by changing the pH of the flows within the microchannels. The laminar flow conditions within the device result in a pH gradient at either interface of the central flow, where diffusion of hydrogen ions enables the deprotonation of the PDPA block copolymer and results in self-assembly of polymersomes. Dynamic light scattering reveals hydrodynamic diameters in the range of 75-275 nm and double membrane structures visualized using transmission electron microscopy indicate that polymersome nanostructures are being produced. The encapsulation efficiency for Bovine Serum Albumin (BSA) was calculated by measuring the spectroscopic absorbance at 279 nm and indicates that the encapsulation efficiency produced in the microfluidic device is equivalent to the standard in solution production method. Critically, the microfluidic system eliminates the use of organic solvents, which limit biological applications, through the pH induced self-assembly process and offers a continuous production method for intracellular delivery polymersomes.

Chapter 2 - Mechanisms of air bubble entrainment

Numerous studies have investigated how liquid water behaves on solid surfaces with uniformly hydrophilic or uniformly hydrophobic wetting properties. In particular, uniformly hydrophobic surfaces have been widely studied for modifying flow behavior of rivulets and drops at smaller scales, as well as for drag reduction on ships or other free-surface-piercing bodies at larger scales. Despite the extensive body of work on surfaces with uniform wetting properties, minimal work has been done to investigate how combining hydrophilic and hydrophobic regions onto a single surface to create macroscopic non-uniform wetting properties affects flows. Research in this vein has predominantly focused on low Reynolds number flows, such as in microfluidic channels or droplet impacts. This thesis expands on the current literature by investigating contact line dynamics and global flow behavior on surfaces with larger-scale non-uniform wetting properties. Experiments were first carried out to study thin sheet flow down an inclined plate at Re ~ 50 - 1200. The plate's wetting condition was changed by introducing alternating hydrophilic and hydrophobic bands 2-25 mm wide oriented at different angles with respect to the flow direction. Results show that the contact line of such flows is heavily modified compared to the uniform cases. At low Reynolds numbers, large-scale wettability heterogeneities are observed to tune the fingering instability wavelength if the bands are parallel to the flow direction and to dampen finger oscillations if the bands are perpendicular to the flow direction. At higher Reynolds numbers, roller structures are introduced at every hydrophilic-to-hydrophobic junction, modifying the global flow morphology. Entrained air bubbles are also captured and observed to coalesce if the bands are perpendicular to the flow direction. These experiments were then extended to a surface-piercing hydrofoil coated with alternating hydrophilic and hydrophobic bands. Experiments were run in Caltech's Free Surface Laboratory water tunnel for Re on the order of 104 to 105. The experiments demonstrate that the contact line is modulated in this context, alternating from concave to convex over the different wettability regions. The modulation of the contact line propagates to the rest of the water free-surface via the generation of standing waves and further modifies the free-surface separation point's location and steadiness. In addition, changes in wettability are observed to generate side force, which is of interest for vessel maneuvers in naval applications.

A green microfluidic method for the simultaneous extraction of polar and non-polar basic compounds in biological samples

Polycaprolactone nanoparticles (PCL NPs) were produced by a liquid nonsolvent nanoprecipitation process in a flow‐focusing microfluidic device and optimized in terms of particle size, polydispersity index (PDI), and zeta potential ζ. The effects of flow rate ratio (FRR), total flow rate (TFR), the organic solvents tetrahydrofuran and dimethylformamide (DMF), the surfactants polyvinyl alcohol and Tween 80, and polymer molecular weight on the size, PDI, and ζ of PCL NPs were investigated. A stability study was performed to compare the effect of the surfactants on the characteristics of PCL NPs over 7 d. The smallest particles are produced at the highest FRR, TFR, and polymer molecular weight and lowest polymer concentration in DMF. The presence of both surfactants results in smaller NPs.